Any prospect of Manny Pacquiao meeting Floyd Mayweather Jr may hinge on how the former fares against Timothy Bradley, with the Filipino's trainer Freddie Roach claiming his charge will retire if he "looks bad" on June 9.

Pacquiao puts his WBO welterweight title on the line against the unbeaten Bradley in Las Vegas on Saturday, with the 33-year-old keen to silence those questioning whether his skills are diminishing after he scraped a contentious points victory over Juan Manuel Marquez last November.

Should Pacquiao (54-3-2) successfully defend his belt, and look good in the process, calls for the Filipino to face pound-for-pound rival Mayweather, who is currently serving a jail sentence for domestic violence, will intensify.

However, Roach has warned that a showdown with the unbeaten Mayweather is unlikely to materialise if Pacquiao fails to deliver a top performance against Bradley at the weekend.

"Bradley's no killer, but he tries hard," Roach said, according to the Associated Press. "Manny should eat him up as he comes forward. I think Manny should look really good in this fight.

"If he looks bad, he retires. At least I'll tell him to. And he may be the first one who will listen to me."